The invention pertains to a cutting tool which has a cobalt cemented tungsten carbide substrate with a strongly adherent diamond coating thereon.
In the past, brazed-on polycrystalline diamond (PCD) tipped cutting inserts and cutting inserts, which had have a chemical vapor deposition (CVD) diamond coating, have been used for material removal in certain applications. The workpiece materials for these material removal applications included free-machining aluminum alloys, high silicon aluminum, nonferrous materials (e.g., copper, bronze, and brass), ceramics materials, fiber-reinforced materials, graphite laminates, nylons, acrylics, phenolic resin materials, metal matrix composites (e.g., silicon carbide or alumina in an aluminum matrix), plastic, rubber and wood. While these PCD cutting inserts performed acceptably, these cutting inserts had an inherent disadvantage in that there was only one cutting edge per cutting insert. This was in contrast to a CVD diamond coated cutting insert which had multiple cutting edges, such as shown in U.S. Pat No. 5,585,176 to Grab et al. (assigned to Kennametal Inc. of Latrobe, Pa., the assignee of the present patent application). While these earlier CVD diamond coated cutting inserts have performed in an acceptable fashion, there remains the need to develop other processes to produce diamond coated cutting inserts, as well as diamond coated cutting inserts produced by these other processes, which possess the requisite properties to perform in a satisfactory fashion. These properties include that the coating be strongly adherent to the substrate so as to avoid premature flaking, that the thickness of the coating be sufficiently great so as to provide for adequate tool life, and that the sharpness of the cutting edges being sufficiently sharp so as to provide for an acceptable workpiece surface finish (i.e., an acceptable surface roughness).
In one form thereof, the invention is a coated body which has a substrate made of tungsten, carbon, and cobalt. The substrate presents a surface. Eta phase is present at the surface of the substrate. Fibrous tungsten carbide grains are present at the surface of the substrate. The surface of the substrate has a surface roughness, Ra, of greater than about 12 microinches. A coating layer is on the surface of the substrate.
In another form thereof, the invention is a process for making a coated body comprising the steps of: providing a substrate comprising tungsten, carbon and cobalt wherein the substrate has at least one surface with eta phase thereon; subjecting the substrate with eta phase on the surface thereof to a conversion treatment at a temperature between about 1250xc2x0 C. and about 2000xc2x0 C. under at least a partial vacuum for a duration sufficient as to convert at least a portion of the eta phase to fibrous tungsten carbide grains whereby the fibrous tungsten carbide grains are at the surface so that the substrate surface presents a surface roughness, Ra, of greater than 12 microinches; and applying a coating to the surface of the substrate.
In still another form thereof, the invention is a process for making a coated body comprising the steps of: providing a substrate comprising tungsten, carbon and cobalt; the substrate presenting at least one surface; and the substrate having been subjected to a roughening heat treatment so as to cause grain growth of the tungsten carbide grains so that the surface of the substrate has a surface roughness, Ra, of at least 12 microinches, and the roughening heat treatment causing the reduction o f the concentration of the cobalt at the surface of the substrate; oxidizing the surface of the substrate which has been subjected to the roughening heat treatment so as to form eta phase at the surface of the substrate; subjecting the substrate with eta phase at the surface thereof to a conversion heat treatment at a temperature between about 1250xc2x0 C. and about, 2000xc2x0 C. under at least a partial vacuum for a duration sufficient as to convert at least a portion of the eta phase to fibrous tungsten carbide grains so that the fibrous tungsten carbide grains are at the surface wherein the substrate surface presents a surface roughness, Ra, of greater than 12 microinches; and applying a coating to the surface of the substrate.